Seasonal changes in chlorine and methoxyl content of leaves of deciduous trees and their impact on release of chloromethane and methanol at elevated temperatures
Seasonal changes in chlorine and methoxyl content of leaves of deciduous trees and their impact on release of chloromethane and methanol at elevated temperatures
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DOI：
10.1071/en14208
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发表时间：
2015-07
影响因子：
4.3
通讯作者：
W. C. Mcroberts;F. Keppler;D. B. Harper;J. Hamilton
中科院分区：
文献类型：
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作者：
W. C. Mcroberts;F. Keppler;D. B. Harper;J. Hamilton
环境背景氯甲烷是自然产生的最丰富的含氯有机化合物，约占氯催化的平流层臭氧破坏的16%。这种气体的一个重要来源是生物聚合物果胶和木质素的氯离子和甲氧基之间的反应产生的气体。在几种落叶树种的叶片中观察到的氯和甲氧基库的季节性变化对于理解生物质燃烧过程中氯的挥发和估计全球氯甲烷收支具有重要意义。摘要大气氯甲烷(CH3Cl)对平流层臭氧的破坏起着重要作用。以前的研究表明，这种气体的一个重要来源是在常温和高温(150-350摄氏度)下从树叶和树叶凋落物中排放出来的气体。本研究在2004年和2005年对落叶温带树种白蜡树、山毛榉、挪威枫树和栎树的叶片总氯和OCH3含量进行了测定。总氯含量随着叶龄的增加而增加。总的季节性积累在5到21倍之间，取决于年份和物种。在2004年整个生长季，监测了白蜡树和挪威枫树叶片加热至350℃时的OCH3池以及CH3Cl和甲醇(CH3OH)的释放。CH3Cl的释放量随着叶片氯的积累而线性增加，而CH3OH的排放量没有实质性变化。春季氯向CH3Cl的转化率低于夏季和秋季衰老期，在22%~58%之间。叶片OCH3含量与CH3Cl和CH3OH释放量均无相关性。OCH3转化为CH3OH和CH3Cl总和浓度的百分比在41%到66%之间。植物成分果胶和木质素被确定为CH3Cl和CH3OH中CH3基团的两个主要来源，当贡献甲基部分的OCH3池耗尽时(>；350°C)，排放停止。这些发现对估计生物质燃烧过程中CH3Cl的释放和理解生物质能源生产过程中氯的挥发具有重要意义。
Environmental context Chloromethane is the most abundant naturally produced chlorine-containing organic compound, responsible for ~16% of chlorine-catalysed stratospheric ozone destruction. A significant source of this gas is emission from biomass by reaction between chloride ion and methoxyl groups of the biopolymers pectin and lignin. The seasonal changes in the chlorine and methoxyl pools observed in leaves of several deciduous tree species have implications for understanding chlorine volatilisation during biomass burning and estimation of the global chloromethane budget. Abstract Atmospheric chloromethane (CH3Cl) plays a role in the destruction of stratospheric ozone. Previous studies suggest an important source of this gas is emission from leaves and leaf litter at ambient and elevated (150–350°C) temperatures. In this study, the total chlorine and OCH3 content of leaves of the deciduous temperate tree species ash, beech, Norway maple and oak were measured throughout the 2004 and 2005 growing seasons. The total chlorine content increased with leaf age. The overall seasonal accumulation varied between five- and twenty-one fold, dependent on both year and species. Throughout the 2004 growing season, the OCH3 pool and the release of CH3Cl and methanol (CH3OH) from leaves of ash and Norway maple were monitored on heating to 350°C. The amounts of CH3Cl released increased linearly as leaf chlorine accumulated whereas emissions of CH3OH did not substantially change. Conversion of chlorine to CH3Cl was lower in the spring than during the summer and autumnal senescence period, ranging from 22 to 58%. No correlation was found between leaf OCH3 content and either CH3Cl or CH3OH release. The percentage conversion of OCH3 to the summed concentrations of CH3OH and CH3Cl ranged from 41 to 66%. The plant components pectin and lignin were identified as two major sources of the CH3 group in CH3Cl and CH3OH and emissions ceased when the OCH3 pool contributing the methyl moiety was exhausted (>350°C). These findings have implications for estimation of CH3Cl release during biomass burning and for our understanding of chlorine volatilisation during energy production from biomass.